As is known a scroll compressor generally comprises the following elements:                a housing;        a stator that is immovably affixed in the housing and which comprises a stationary stator scroll with a central stator axis, whereby this stator scroll is formed by a stator strip with two stator flanks that is wound spirally along its length and which is affixed upright with a certain height on a stator plate;        a rotor that is movably affixed in the housing and which comprises a rotor scroll with a central rotor axis, and this rotor scroll is formed by a rotor strip with two rotor flanks that is wound spirally along its length, and which is affixed upright with a certain height on a rotor plate and whereby the rotor scroll and the stator scroll are affixed in one another between the stator plate and the rotor plate;        a low pressure inlet on the outside of the scroll compressor; and        a high pressure outlet in the centre of the scroll compressor; and,        a drive for a movement of the rotor whereby the central rotor axis circles eccentrically around the central stator axis without the rotor hereby undergoing a rotation around the central rotor axis.        
It is also known that in each position of the rotor in the stator during this circling and eccentric movement of the rotor with respect to the stator, places are formed where there is a maximum or minimum opening between the rotor scroll and stator scroll.
It is the case here that these places with a minimum and maximum opening at each position of the rotor with respect to the stator, are located in a plane that comprises both central axes, which will be further clarified in the text on the basis of drawings, whereby this plane will be called the sealing plane hereinafter.
Attention is hereby drawn to the fact that the minimum openings at every moment during the movement of the rotor in fact define compression chambers, but they are not hermetically sealed on account of internal clearances in the scroll compressor, as could be incorrectly thought from the name sealing plane.
The compression chambers continually change shape during the circling eccentric movement of the rotor, whereby air or gas supplied to the outside of the scroll compressor via the inlet is continually pushed more deeply towards the centre of the scroll compressor, where the compression chambers occupy a smaller volume, so that the air or gas is increasingly compressed until the compressed air or gas can finally leave the scroll compressor via the outlet in the centre of the scroll compressor.
It should also be noted that the rotor scroll and the stator scroll, in the places with a minimum opening at each height along the rotor flanks and stator flanks, are located at a certain radial distance from one another whereby these distances can thus be considered as local transverse internal clearances of the scroll compressor.
A transverse internal clearance here means that it is a clearance in the scroll compressor in a direction transverse to the rotor flanks and the stator flanks.
Of course there are also internal clearances between the rotor tip and the stator plate and between the stator tip and the rotor plate, whereby these clearances are further designated in the text as lateral internal clearances.
For a good operation of the scroll compressor all the internal clearances, and in particular the local transverse internal clearances, must remain above a certain minimum value at all times in order to prevent contact between the rotor scroll and the stator scroll.
On the other hand, large internal clearances and in particular large local transverse internal clearances are also undesirable, as this would lead to a large leakage rate and pressure loss in the scroll compressor, with recompression of air or gas and would thus result in extra heat generation such that the efficiency of the scroll compressor is considerably negatively influenced.
In other words it comes down to realising the smallest possible internal clearance in the scroll compressor without running the risk of the rotor scroll coming into contact with the stator scroll during its movement.
A great difficulty here is that the internal clearances in the scroll compressor are far from a static fact.
Indeed, in the transition from an initial stationary state of the rotor, when the scroll compressor is not in use, to a final state during nominal service of the scroll compressor, whereby the rotor is moving at full speed, the pressures of course change significantly, as it is the intention to compress air or gas, as do the temperatures in the scroll compressor.
These changes of pressures and temperatures in the scroll compressor are accompanied by a deformation of the stator scroll and the rotor scroll, whereby the local internal clearances in the scroll compressor change as a result of such deformations.
In order to describe a number of these dynamic phenomena more easily, a number of items will first be defined hereinafter.
From the foregoing it can be concluded that the intersecting lines of the flanks of the stator scroll and the rotor scroll with the stator plate or rotor plate concerned form spiral base edges.
Hereby the geometric location of the points through which a perpendicular line on the stator plate or rotor plate intersects in an aforementioned spiral base edge determines spiral flanks, that will be called the ideal spiral flanks hereinafter.
In brief, the ideal spiral flanks are flanks that are perpendicular to the rotor plate and stator plate, so that there is a constant internal clearance viewed over the height of the flanks in the given situation, at least insofar the rotor plate and stator plate are parallel to one another, which is of course the intention.
Furthermore, in the text the terms “local rotor flank deviation” and “local stator flank deviation” are used as referring to the radial distance from a point on an ideal spiral flank of the rotor scroll or stator scroll to the closest point on the corresponding spiral flank of the rotor scroll or stator scroll respectively, whereby a local rotor flank deviation or a local stator flank deviation has a positive sign when the deviation is directed in a direction away from the central axis concerned, or thus when the distance between the point concerned and the central axis concerned is greater than the distance between the corresponding point on the ideal spiral flank and the central axis concerned.
In the reverse case whereby the deviation is directed towards the central axis, the rotor flank deviation or stator flank deviation concerned will have a negative sign.
Moreover, in general it can be said that a local transverse internal clearance in a minimum opening is composed of an interjacent basic clearance defined by the radial distance in the sealing plane between the ideal spiral flanks located closest to the flanks concerned and of a local clearance deviation.
In brief every local transverse internal clearance can be described as the sum of a desired ‘ideal’ basic clearance and a local clearance deviation that is due to local deviations of the rotor scroll and the stator scroll in the sealing plane concerned with respect to the ideal spiral flanks.
Hereby the local clearance deviation is the difference between a local rotor flank deviation and a local stator flank deviation.
More specifically, the local rotor flank deviation and the local stator flank deviation respectively, which form the local clearance deviation concerned, are the deviations of the rotor scroll and the stator scroll with respect to the ideal spiral flank at the location of the points of the rotor flank concerned and the stator flank concerned that are located at the height concerned of the local transverse internal clearance concerned, and which moreover are located in the sealing plane concerned.
When going from a stationary state of the rotor to a state in nominal service after starting the scroll compressor, the pressures and temperatures in the scroll compressor change resulting in a deformation of the stator scroll and the rotor scroll and a change of the local stator flank deviations and local rotor flank deviations, thus of the local transverse internal clearances.
In order to facilitate the use of words in this text, a state of the scroll compressor and its elements when stationary is designated by the adjective ‘initial’, while a state of the scroll compressor and its elements during nominal operation is further designated by the adjective ‘final’.
Of course there is nothing ‘initial’ or ‘final’ about the states concerned, whereby more specifically attention must be drawn to the fact that in the ‘final’ state in nominal service the rotor is moving at full speed and the various elements of the scroll compressor in this final state thus take on a multitude of instantaneous forms and instantaneous positions.
Furthermore, it can be said that that the local transverse internal clearances for each position of the rotor when the scroll compressor is stationary at ambient temperature and ambient pressure present a clearance profile over the height, hereinafter termed the initial or stationary clearance profile, while these local transverse clearances for each position of the rotor during nominal service of the scroll compressor at operating temperature and operating pressure present a different instantaneous clearance profile over the height, hereinafter termed an instantaneous final clearance profile or an instantaneous circulating clearance profile.
Generally it is the case that in the known scroll compressors the stator scroll and the rotor scroll are constructed with a constant thickness, whereby the two flanks of each scroll are perpendicular to the rotor plate or stator plate concerned, at least when the scroll compressor is stationary and at normal ambient temperatures and ambient pressures, so that the flanks of the stator scroll and the rotor scroll coincide with the ideal spiral flanks when stationary.
In brief, with such known scroll compressors the initial local rotor flank deviations and initial local state flank deviations when the known scroll compressor is stationary are as good as zero, so that in the minimum openings during stoppage there are also no initial local clearance deviations, irrespective of the position of the rotor and irrespective of which sealing plane it concerns.
Hereby the flanks of the stator scroll and the rotor scroll of the known scroll compressor when stationary are parallel or as good as parallel to one another, whereby the stationary clearance profile of the local transverse internal clearances in a sealing plane presents little or no variation, or in other words, whereby at each height in the sealing plane concerned the initial local transverse internal clearance is just as large and equal to the aforementioned basic clearance.
In a final state of the scroll compressor in nominal service, the stator scroll and the rotor scroll take on different instantaneous final forms, compared to the initial form when stationary, whereby the instantaneous local transverse clearances in a sealing plane are composed of a final aforementioned basic clearance and an instantaneous final (or circulating) local clearance deviation, that is a function of the local instantaneous form of the rotor scroll and the stator scroll during nominal service of the scroll compressor.
Hereby during nominal operation of the scroll compressor the pressures and temperatures in its centre, where the outlet of the scroll compressor is also located, are the highest, while the pressures and temperatures in the scroll compressor decrease in the more radially outward parts of the scroll compressor.
Moreover, it is the case that cooling fins are generally provided on the side of the rotor plate and the stator plate, opposite the rotor scroll and stator scroll respectively.
A consequence of this is that the base of the rotor scroll and the base of the stator scroll are better cooled than the tip of the rotor scroll and the tip of the stator scroll, such that during nominal service of the scroll compressor a temperature gradient consequently prevails over the height of the rotor scroll and over the height of the stator scroll, with an increasing temperature towards their tips.
All these pressure and temperature effects, more specifically pressures and temperatures that decrease from the centre to the outside, and temperatures that increase from the base to the tip of the scroll concerned, mean that the rotor scroll and the stator scroll tend to deform, such that the rotor tip and the stator tip bend away from the centre towards the outside of the scroll compressor.
Depending on the position in the scroll compressor, in a minimum opening, a rotor tip for example can thus tend towards the opposite stator base, while on the contrary the opposite stator tip at this position tends away from the rotor base at this position.
Analogously, depending on the position in the scroll compressor, a stator tip can tend towards the opposite rotor base, while on the contrary the opposite rotor tip at this position tends away from the stator base at this position.
A consequence of this is that the local transverse internal clearance at certain heights in an instantaneous sealing plane during nominal operation of the scroll compressor can be greatly decreased, compared to the local transverse internal clearance at this height in the same sealing plane when the scroll compressor is stationary.
On the other hand it is also possible that at other heights in the same instantaneous sealing plane concerned, this local transverse internal clearance during operation of the scroll compressor has increased compared to the local transverse internal clearance at this height in the same instantaneous sealing plane when the scroll compressor is stationary.
This means that under the effects of the pressures and temperatures, the local instantaneous transverse internal clearance during nominal operation of the scroll compressor can easily become all too small at certain positions of the rotor in the stator when nothing is done.
With known scroll compressors this problem is solved by making the initial clearances, when the known scroll compressor is stationary, sufficiently large.
In addition it is the case that at places where the local transverse internal clearance increases during operation of the scroll compressor, the internal leakage rate and the internal pressure loss between compressor chambers of the scroll compressor increase.
With known scroll compressors, this phenomenon is further reinforced by the aforementioned measure whereby the clearances in the scroll compressor when stationary are made large to ensure a minimum local transverse internal clearance at all heights of the stator scroll and rotor scroll during nominal operation of the scroll compressor.
In brief, the internal clearances in a scroll compressor during nominal operation greatly affect the efficiency of the scroll compressor, and with the known scroll compressors it can be difficult to stay within the bounds and/or the circulating clearance profile of the local transverse internal clearances in the scroll compressor is highly variable or can be difficult to evaluate beforehand.
This problem is all the more acute as the pressures and temperatures in the scroll compressor rise, the powers increase or the speed of motion of the rotor in the stator increases.